On 25 Jan 2024, at 9:56, Jorge Mora wrote:
> A call to listxattr() with a buffer size = 0 returns the actual
> size of the buffer needed for a subsequent call. When size > 0,
> nfs4_listxattr() does not return an error because either
> generic_listxattr() or nfs4_listxattr_nfs4_label() consumes
> exactly all the bytes then size is 0 when calling
> nfs4_listxattr_nfs4_user() which then triggers the following
> kernel BUG:
>
> [ 99.403778] kernel BUG at mm/usercopy.c:102!
> [ 99.404063] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
> [ 99.408463] CPU: 0 PID: 3310 Comm: python3 Not tainted 6.6.0-61.fc40.aarch64 #1
> [ 99.415827] Call trace:
> [ 99.415985] usercopy_abort+0x70/0xa0
> [ 99.416227] __check_heap_object+0x134/0x158
> [ 99.416505] check_heap_object+0x150/0x188
> [ 99.416696] __check_object_size.part.0+0x78/0x168
> [ 99.416886] __check_object_size+0x28/0x40
> [ 99.417078] listxattr+0x8c/0x120
> [ 99.417252] path_listxattr+0x78/0xe0
> [ 99.417476] __arm64_sys_listxattr+0x28/0x40
> [ 99.417723] invoke_syscall+0x78/0x100
> [ 99.417929] el0_svc_common.constprop.0+0x48/0xf0
> [ 99.418186] do_el0_svc+0x24/0x38
> [ 99.418376] el0_svc+0x3c/0x110
> [ 99.418554] el0t_64_sync_handler+0x120/0x130
> [ 99.418788] el0t_64_sync+0x194/0x198
> [ 99.418994] Code: aa0003e3 d000a3e0 91310000 97f49bdb (d4210000)
>
> Issue is reproduced when generic_listxattr() returns 'system.nfs4_acl',
> thus calling lisxattr() with size = 16 will trigger the bug.
>
> Add check on nfs4_listxattr() to return ERANGE error when it is
> called with size > 0 and the return value is greater than size.
>
> Fixes: 012a211abd5d ("NFSv4.2: hook in the user extended attribute handlers")
> Signed-off-by: Jorge Mora <mora@xxxxxxxxxx>
Reviewed-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
Ben
